1. Field of the Invention
The invention relates generally to a circuit for central controlled telecommunications exchange systems, and specifically to PCM time division multiplex (TDM) telephone exchange systems, in which a central switching network, which serves to switch through the connections, together with a program-controlled central processor, one of the functions of which is to control the switching network and to process switching information, is provided in duplicate as a stand-by operating facility. A plurality of decentralized groups of terminals are each equipped with a subsidiary switching network for the external connection of connection lines and/or subscriber lines, and with a decentralized, programmable control device which functions to receive switching information from these lines, to preliminarily process the switching information and forward it to the central processor, and to transmit switching information to these lines. In each of the groups of terminals, the respective subsidiary switching network is internally connected via two groups of link lines which are divided up in groups, to switching network terminals of the first of the two parallel switching networks and to the other thereof for a data exchange, for the purpose of handling of switching information and for the transmission of program software and switching software between the decentralized control devices and the respective processor which is ready for operation or is preparing for operation. Each decentralized control device data connection from the processor via the assigned switching network to the decentralized control devices is brought into or maintained in the ready-for-operation state. An input-output device is provided which is connected to the central processor and which is permanently connected by a plurality of link terminals, provided for each data connection, to switching network terminals individually in the manner of the link lines.
2. Description of the Prior Art
A known prior art circuit is described in the magazine "Telcom Report" supplement 1981, pages 7 ff, 19 ff and 49 ff which illustrates and describes the subsidiary switching networks of the peripheral terminal groups (LIU). Internally they are connected to the duplicated central switching network and externally they are connected via terminal units (LTU/DIU) to analog lines and analog channels of digital transmission systems. Except where they serve as subscriber lines or channels provided for subscriber terminals, these lines and channels lead to other exchanges and can be seized in known manner for the establishment of individual connections.
The control channels which are permanently switched through into the ready-for-operation state via the duplicating switching network are described in page 8. Therefore, for reasons of security, the central switching network and central processor are provided in duplicate. This duplication is not of particular significance as regards the totality of such an exchange as it relates to only a few central components. Thus the peripheral terminal groups and the assigned components, such as the decentral control unit and subsidiary switching network, which are provided in larger numbers and consequently on a comparatively larger scale, are not provided in duplicate. In the event of the breakdown of a terminal group (for example of its subsidiary switching network or its decentral control device or its current supply), such a relatively small part of the total number of connected subscriber lines and connection lines is affected that a temporary interruption in operation, which is limited to these lines can be accepted.
The control channels consist of the aforementioned data connections which must be provided for the data exchange which serves to process incoming information in the terminal groups, in the central processor and to transmit program software and switching software from the central processor to the decentral control units, and which is carried out between the decentral control devices and the central processor and which for this purpose are brought or permanently maintained in the ready-for-operation state. In the aforementioned Telecom Report, page 25 it is described that at the start of the switching operation, the decentral control devices are loaded with programs and permanently stored data from the central processor via the control channels Such loading procedures are carried out for each of the decentral control devices. The loading procedures are carried out not only at the start of the switching operation but also for the purpose of stand-by operation. Thus when the switching operation which is employing one of the two parallel switching networks and one of the two central processors, i.e. the central processor assigned to the respective central switching network, is continued not using this central switching network and this central processor, it uses the respective other central switching network and the respective other central processor.
Stand-by operation is required when faults occur, and thus generally unforseeably. Faults can be sufficiently serious to necessitate immediate stand-by operation. Frequently, however, such faults affect only parts of the common exchange for example only a part of the central switching network or only specific functions in the central switching network or in the central processor or else they may occur sporadically. In such cases, i.e. in most cases where there is a need for stand-by operation, the stand-by operation measure can also be temporarily postponed. As the above-described loading procedures associated with stand-by operation involve large quantities of data and must be carried out in respect of each decentral control device, they are relatively time consuming. The loading procedures must be completed before the switching operation itself can be commenced. Stand-by operation measures often result in a disadvantageously long interruption in operation.
Therefore, the object of the present invention is to provide improved operating conditions for stand-by measures and to avoid long interruptions in operation.